<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .div1 {
            width: 0px;
            border-style: solid;
            border-width: 100px;
            border-top-color: red;
            border-right-color: blue;
            border-bottom-color: yellow;
            border-left-color: black;
        }

        .div2 {
            width: 0px;
            border-style: solid;
            border-width: 100px;
            border-color: transparent transparent yellow transparent;
        }
    </style>
</head>
<body>
<div class="div2">

</div>
<div class="div1">

</div>
</body>
</html>